Fish slaughter

Fish slaughter is the process of killing fish, typically after harvesting at sea or from fish farms. At least one trillion fish are slaughtered each year for human consumption. Some relatively humane slaughter methods have been developed, including percussive and electric stunning. However, most fish harvesting continues to use methods like suffocation in air, carbon-dioxide stunning, or ice chilling that are widely regarded as inhumane.

According to the Food and Agriculture Organization (FAO), a total of 156.2 million tons of fish, crustaceans, molluscs, and other aquatic animals were captured in 2011. This is a sum of 93.5 million tons of wild animals and 62.7 million tons of farmed animals. 56.8% of this total was freshwater fish, 6.4% diadromous fish, and 3.2% marine fish, with the remainder being molluscs, crustaceans, and miscellaneous.[1]

The number of individual wild fish killed each year is estimated as 0.97-2.74 trillion (based on FAO tonnage statistics combined with estimated mean weights of fish species).[2] The FAO numbers do not include illegal, unreported and unregulated fishing, nor discarded fish. If these are included and over-reporting by China subtracted, the totals increase by about 16.6% to 33.3%.[2] A similar estimate for the number of farmed fish slaughtered each year is 0.037 to 0.120 trillion.[3]

Mid-sized trout farms in the UK may process more than 10,000 fish per hour. They are often operated by only a few people, and it may be necessary to kill trout on short notice or even at night.[4]

Following electric stunning, as fish gradually resume consciousness, they begin to make rhythmic gill-cover movements. Based on EEG correlations, it is believed that stunned fish remain insensible until they have resumed rhythmic gill patterns.[6] This can be used as a convenient assessment tool for the effectiveness of electric stunning.[4]

This is the oldest slaughter method for fish and is considered inhumane because it can take the fish over an hour to die.[5] One Dutch study found that it took 55-250 minutes for various species of fish to become insensible during asphyxiation.[9] Fish that evolved for low-oxygen environments take longer to die. At higher temperatures, fish lose consciousness more quickly.[10]

Meat quality and shelf-life are also diminished when this method is used.[5]

Also called live chilling, this method involves putting fish in baths of ice water, where they chill and eventually die of anoxia. Because chilling slows metabolic rate and oxygen needs, it actually prolongs the duration until death, with some species taking more than an hour to die.[5] On these grounds, the Farm Animal Welfare Council's 1996 report on farmed-fish welfare stated: "The cooling of live trout on ice after they have been removed from water should be prohibited."[11] In contrast, later research suggested that for warm Mediterranean species such as sea bream and sea bass, the method might at least be preferable to air asphyxiation, with fish showing lower levels of stress indicators.[5]

Most often applied for salmon and trout, CO2 narcosis involves filling the fish water with CO2 to produce acidic pH, which injures the brain. The procedure is apparently painful, as evidenced by fish swimming vigorously and trying to escape from the tank. CO2 immobilizes the fish within 2–4 minutes, but the fish remain conscious until subsequent stunning or killing.[5]

Exsanguination is the process whereby an animal is cut so that it bleeds to death. Fish are cut in body regions containing numerous nociceptors (pain receptors), and the process elicits fear and panic unless the animals are unconscious. If not stunned, according to behavioral and neural criteria, fish may remain conscious for 15 minutes or more between the time when major blood vessels have been cut and when they lose consciousness.[7][12] Eel brains may continue to process information for 13–30 minutes after being decapitated, and some fish may remain sensible for 20–40 minutes after evisceration.[13]

Also known as knocking, percussive stunning involves hitting the fish's head with a wooden or plastic club, called a priest. One or two appropriate blows can disrupt the brain sufficiently to render the fish insensible and potentially even kill it directly. However, applying this method correcly requires training and effort. Percussive stunning must be applied one fish at a time and so is typically only used for large fish, such as salmon and trout. If the operator is skilled, percussive stunning can be among the most humane methods and can also yield high meat quality.[5] One comparison of slaughter methods found that percussive stunning had the best welfare performance as measured by low hematocrit, low plasma glucose, low lactate, and high muscle energy charge.[14]

For some fish species, there are automated percussive stunning tools, such as a pneumatic club for salmon.[5] However, building an automated machine to process, orient, percussively stun, and bleed bulk quantities of small fish would be difficult.[4]

Pithing, also known as ikejime, involves sticking a sharp spike through the brain of the fish. If done properly, it can kill quickly, however, if the operator misses the brain, the results may be traumatic for the fish. As with percussive stunning, spiking is used to kill one fish at a time and so is mainly used for large species such as tuna and salmon.[5]

Electricity can be more humane than alternatives if applied correctly.[15] In addition to potentially producing unconsciousness quickly, stunning reduces the stress of restraint and being removed from water.[7]:167-68

If electrical parameters are not optimized, electrical stunning may produce immobility without loss of consciousness, which is inhumane.[5][13][7]:167 There isn't much public data comparing optimal stun settings found by researchers with the settings used in commercial slaughter operations, so it's unknown how effective real-world stunning is.[16]:7 In addition, proper stun parameters vary significantly by species.[7]:168

Electricity may introduce bleedspots, so proper settings are required.[15]

Systems have been developed to slaughter large numbers of fish whilst maintaining welfare standards. Jeff Lines and his collaborators observed that previous electrical stunning methods had been either too aggressive (resulting in hemorrhages and broken bones that reduced meat quality) or too lax (meaning that the fish were unlikely to be rendered unconscious). They determined that stunning for 60 seconds in an electric field of 250 V/m r.m.s. with a sinusoidal waveform of 1,000 Hz was capable of rendering trout permanently unconscious without degrading meat quality.[4] Further research in the UK developed a commercial-quality stunning system called HS1. This system includes an 18-meter tube into which the fish are placed. They are first stunned and then passed along to maintenance tubes that keep them unconscious. The machine determines the appropriate voltage based on water conductivity. HS1 is designed to process 6 tons of fish per hour. The machine is widely adopted in the UK and now an estimated 80% of UK trout are stunned using it.[17] According to the Humane Slaughter Association's James Kirkwood: "Before ten years ago there was no way to humanely kill farmed fish en masse – they died slowly through suffocation when harvested from the water. This welfare benefit affects millions of fish."[18]

^ abcdeEFSA (11 October 2004). "Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals". The EFSA Journal. doi:10.2903/j.efsa.2004.45.|accessdate= requires |url= (help)